1. Technical Field
The disclosure relates to a structure of a flat speaker.
2. Background Art
The two most direct sensory systems of human being are visual and audible systems, so for a long time, scientists have given great effort to developing related elements or system techniques. Currently, electro-acoustic speakers are mainly classified into direct and indirect radiating types, and are approximately classified into dynamic, piezoelectric, and electrostatic speakers according to driving methods.
Electrostatic speakers mainly include hi-end earphones and loudspeakers in the current market. The operating principle for conventional electrostatic speakers is that two electrodes which are fixated and have holes are used to clamp a conductive membrane to form a capacitor, a DC bias is applied to the membrane and an AC voltage of sound frequencies is applied to the two fixated electrodes, and electrostatic forces generated by positive and negative electric fields are used to drive the conductive membrane to vibrate and to radiate sounds. The bias of the conventional electrostatic speakers is as high as hundreds to thousands of volts, so that expensive and bulky amplifiers need to be externally connected. Hence, the above is the reason that the conventional electrostatic speakers are not popular. If the electrostatic speakers cooperate with structural designs of membranes that are ferroelectric, although the AC voltage of the sound frequencies is lowered, the electrostatic effects of the membrane causes the electrode and the membrane to contact each other and thereby inhibiting sound production.
Relating to electrostatic speakers, U.S. Pat. No. 3,894,199 discloses an electro-acoustic transducer, as shown in FIG. 1, which is a schematic view showing an electro-acoustic converter according to U.S. Pat. No. 3,894,199. A frame holding member 110 made of an insulating material holds two fixated electrodes 120. A membrane 130 is disposed between the two electrodes 120. A plurality of holes 121 are disposed in the electrodes 120 to allow sounds to radiate through. A polarization voltage 141 passes through the membrane 130, each of the electrodes 120, a step-up transformer 140 and an resistor 142. A primary winding 143 of the step-up transformer 140 is connected to a signal source 150. Voltages of the two electrodes 120 are supplied by an AC signal of the signal source 150. The voltages of the two electrodes 120 are opposite, meaning that one is positive and the other is negative.
As illustrated in the related art, the frame holding member 110 is only used to hold the electrodes 120, and there are no supporting members between the membrane 130 and the electrodes 120, so that unintended contact between the electrodes 120 and the membrane 130 cannot be prevented. It can be known that present flat speakers do not provide design descriptions relevant to supporting members.
In addition, the conventional electrostatic speaker have weaker capacity for generating sounds of lower frequencies (<500 Hz), so that the electrostatic speakers on the market are mostly collocated with a dynamic speaker having low frequency response. Hence, it is known that improving low sound pressures at low frequencies of the conventional electrostatic speakers is an important issue in the field.